The objective of the current proposal is to define mutations causing the human factor X deficiency. The nucleotide polymorphisms in normal individuals and patients suffering from factor X deficiency will be identified by restriction endonuclease analysis as well as by the RNA:DNA hybrid analysis. They will be compared to distinguish the mutations specifically related to the disease from the normal polymorphisms. Mutant alleles will be identified by family studies. Mutations which cannot be identified by the above methods will be detected by cloning and sequencing the human factor X genes from factor X deficient individuals and comparing them with the normal factor X gene sequences. Cloning will be accomplished by using lambda vectors. Nucleotide sequences will be established by Maxam and Gilbert method as well as by the dideoxy sequencing method and analysed by various computer programs. After identifying the mutations specifically related to the disease we will determine which of the nucleotide changes are actually etiologic in producing the disease by functional analysis.